The invention relates to a circuit arrangement for operating a high pressure discharge lamp equipped with                input terminals for connection to the poles of a supply voltage source        a DC-DC-converter coupled to the input terminals and comprising                    an inductive element L1,            a unidirectional element D1,            a switching element S1,            output terminals,            a first control circuit coupled to a control electrode of the switching element S1 for generating a control signal for rendering the switching element S1 alternately conductive and non-conductive,            a second control circuit, coupled with the first control circuit for controlling the level of an output voltage of the DC-DC converter that is present between the output terminals,                        a DC-AC-converter coupled to the output terminals and equipped with lamp connection terminals for generating an AC lamp voltage out of the output voltage.        
Such a circuit arrangement is known from DE 10025610 A1. During the starting phase (the phase between ignition and run-up) of the high pressure discharge lamp (further also indicated as lamp), the discharge in the high pressure discharge lamp has not yet become stable. To keep the discharge alive, a comparatively high output voltage is needed. This comparatively high output voltage, however, leads to a relatively high power dissipation in the circuit arrangement after the starting phase, when the high pressure discharge lamp is in stationary operation.
The invention aims to provide a circuit arrangement for operating a high pressure discharge lamp that effectively stabilizes the discharge during the starting phase and has a comparatively low power dissipation during stationary lamp operation.